High-current furnace transformer

ABSTRACT

Electrical inductive apparatus having high-current secondary bushings. The secondary bushings are mounted on the casing of the apparatus in a triangular pattern. The arrangement of the bushings conveniently permits interconnection of the bushings by bus conductors to provide a delta closure for the apparatus.

United States Patent Mitchell, Jr. et al.

[ HIGH-CURRENT FURNACE TRANSFORMER [72] Inventors: George F. Mitchell, Jr., Sharpsville; Robert D. Morris, Sharon; Michael Nevinsky, both of Sharon, all of Pa.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: June 30, 1971 [2]] Appl. No.: 158,369

[52] US. Cl. ..336/90, 336/94, 336/192 [51] Int. Cl ..H0lf 27/62 [58] Field of Search ..336/90, 94, 192

[ 56] References Cited UNITED STATES PATENTS 3,275,900 9/1966 Leonard ..336/90 X 1451 Aug. 1,1972

Primary Examiner-E. A. Goldberg Att0rneyA. T. Stratton et al.

[57] ABSTRACT Electrical inductive apparatus having high-current secondary bushings. The secondary bushings are mounted on the casing of the apparatus in a triangular pattern. The arrangement of the bushings conveniently permits interconnection of the bushings by bus conductors to provide a delta closure for the apparatus.

11 Claims, 10 Drawing Figures PKTENTEDws H972 A 3.681. 728 SHEET 2 OF 4 FIG.4.

1 HIGH-CURRENT FURNACE TRANSFORMER BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates, in general, to high-current furnace transformers and, more specifically, to the arrangement of the secondary bushings on the transformer casing.

2. Description of the Prior Art High-power furnace transformers are used in a variety of industrial applications which require relatively high currents at relatively low voltages. An important application for furnace transformers involves the supplying of power for resistance heated electric furnaces. Due to the fact that the secondary phase windings of three-phase furnace transformers are usually connected in delta, a terminal from each end of a phase winding must be available. Since industrial applications of furnace transformers require various voltage and current ratings, the secondary windings of furnace transformers usually consist of the three separate phase windings, each of which is formed by interconnecting a plurality of separate windings in parallel and/or series combination. This requirement makes it necessary to have both terminals of each separate winding available so that they may be conveniently interconnected. Because of the high currents involved, it is standard practice to bring the terminals of each separate winding to the outside of the transformer casing so that interconnection may be made with bus conductors.

Conventional high-current furnace transformers have the secondary bushings attached to the casing cover plate. The cover plate also usually supports the high-voltage bushings. The bushings are positioned on the cover plate so that they are in line, that is, the middle bushing is aligned directly between the two end bushings. Since one or more of the bus conductors which form the delta closure must be connected between each and every bushing, the length of the bus conductors from one of the end bushings to the middle bushing is considerably shorter than a bus conductor connecting both end bushings. Because of the high currents, bus conductors of unequal length tend to unbalance the secondary circuits.

It is also necessary to bend the bus conductors several times to make the delta closure. The bus conductors must be bent not only to provide adequate spacing from another bus conductor, but must be bent up-over and back-down to provide a crossover of the bus conductors. Thus, this conventional bushing arrangement requires rather complicated bus conductor arrangements which occupy a relatively large amount of space. Additionally, they provide an unbalanced delta closure and, because of the complexity of the arrangement, the bus conductors must be fabricated in the field during installation. It would be desirable, therefore, to provide a secondary bushing arrangement which would permit the making of a substantially balanced delta closure within a minimum of space and with the use of prefabricated bus conductors.

SUMMARY OF THE INVENTION This invention discloses a new and useful arrangement of the secondary bushings on the transformer casing which overcomes the disadvantages of prior art arrangements. The high-current secondary bushings are arranged in a triangular pattern with their orientations and terminal locations such that the connections between the bushings may be made more economically than with prior art arrangements, without sacrificing mechanical or electrical characteristics. The bus conductors which form the delta closure may be connected between the bushings without crossing over other bus conductors with compound bends. The space required to make the delta closure is reduced. The length of the bus conductors are more nearly equal than in prior art arrangements, thus providing a better electrically balanced closure. Due to the simplicity of the bends involved, the bus conductors may be prefabricated at the factory and installed in the field, thereby reducing the chance of incorrect connections.

BRIEF DESCRIPTIONS OF THE DRAWINGS Further advantages and uses of this invention will become more apparent when considered in view of the following detailed description and drawings, in which:

FIG. 1 is a perspective view of a high-current furnace transformer illustrating a secondary bushing arrangement as taught by this invention;

FIG. 2 is a partial perspective view of the secondary bushings shown in FIG. 1 illustrating a placement of the bus conductors for delta closure as taught by this invention;

FIG. 3 is an electrical schematic diagram of the delta closure shown in FIG. 2;

FIG. 4 is a schematic diagram showing the physical and electrical arrangements of the delta closure shown in FIG. 2;

FIGS. 5, 6, 7, 8, 9 and 10 are schematic diagrams showing the physical and electrical arrangements of other delta closures as taught by this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the following description similar reference characters refer to similar members or elements in all figures of the drawings.

Referring now to the drawings and FIG. 1 in particular, there is shown a high-power transformer constructed according to the teachings of this invention. The high-voltage bushings l0, l2 and 14 are attached to the transformer casing cover plate 16. A pressure release device 18 is also attached to the cover plate for safety purposes. The transformer casing front wall 20 and the transformer casing side wall 22 are reinforced by the tank braces 24. A tap changing mechanism 26 is shown attached to the back wall of the transformer casing. It may be used to regulate the output of the furnace transformer. The transformer is mounted on the frame 28 and is connected to a cooling means, such as the oilto-water heat exchanger 30.

The secondary bushing assembly 32 comprises the phase bushings 34, 36 and 38 and their associated supporting member 40 which is attached to the wall 20 of the transformer casing. Each bushing is constructed in a housing member 42 which includes a flange 44 which is attached to the supporting member 40 by the bolts 46. The bushing terminals 48 are embedded in an insulating material 50 and extend through the bushing body to a point within the transformer casing where they are connected to the winding leads. The bushing terminals 48 are substantially flat bars which are constructed of a conducting material, such as copper. The size of the bushing terminals 48 is dependent upon the class and rating of the furnace transformer. Although each bushing is shown having six terminals, the number of terminals may be changed without departing from the teachings of the invention. In general, there will be two bushing terminals for each separate phase winding.

The bushings are positioned on the supporting member 40 in a triangular arrangement. This novel arrangement permits the making of a relatively simple delta closure compared to previous arrangements which use cover plate mounted bushings which are in alignment with each other. A further advantage of placing the secondary bushings 34, 36 and 38 on the front wall is realized by the fact thatthe inner end of the bushings are surrounded by the liquid coolant contained in the transformer casing. This improves the operation of the bushing and improves their efficiency. Conventional cover plate mounted bushings have their lower ends contained in an air space above the oil level.

FIG. 2 is a partial perspective view of the secondary bushing terminals 48 shown in FIG. 1 with a delta closure connected thereto. The bus conductors 52, 54, 56, 58, 60, 62, 64, 66 and 68 are each held against their respective bushing terminal 48 by an insulating spacer 70. A clamping device may be attached to the bushing to compress the terminals, conductors and spacers together and secure the connection, however it is not shown in FIG. 2 for clarity.

Each bushing terminal 48 is connected within the transformer casing to a lead from a separate phase winding. The two ends of the same winding are attached to adjacent bushing terminals forming a bushing terminal pair. Other separate phase windings which have the same phase relationship are connected to the other bushing terminal pairs on the same bushing. Although the bushings shown in FIG. 2 each have three terminal pairs, corresponding to a total of nine separate phase windings, it is within the contemplation of this invention that the number of bushing terminals may be more or less than six. Since the bus conductors which comprise the delta closure are not required to cross each other, the closure may be made without compound bends to cross over another bus conductor. Because of the much simpler bus conductor bends, they may be fabricated at the factory rather than in the field during installation. The cost of the delta closure and the physical space required is minimized by arranging the bushings in a triangular fashion as taught by this invention. The bus conductors are much more similar in length compared to prior art delta closures where the bushings are in alignment.

The triangular placement of the bushings also aids in connecting the secondary of the furnace transformer to the load circuit. Normally, to achieve the proper electrical balance, the bus run from the transformer to the load must be arranged in a triangular pattern. Since the bus conductors of the delta closure are automatically adapted for connection to a triangular array of bus bars, the connection to the load bus run is simplified.

The delta closure effectively forms a set of delta connected secondary windings. FIG. 3 is an electrical schematic representing the delta closure which is shown in FIG. 2. The separate phase windings 72, 74 and 76 have their ends, which are respectively labeled X,, X,, X,, X X and X connected to the terminals 48 of the bushing 34. The separate phase windings 78, and 82 have their ends, which are respectively labeled X X X X X and X connected to the terminals 48 of the bushing 36. The separate phase windings 84, 86 and 88 have their ends, which are respectively labeled X X X,,, X X and X connected to the terminals 48 of the bushing 38. The bus conductors 52, 54, 56, 58, 60, 62, 64, 66 and 68 are schematically shown closing the delta of the secondary windings.

The physical and electrical arrangements of the delta closure shown in FIG. 2 are illustrated schematically in FIG. 4. The terminals 48 of the bushings 34, 36 and 38 are labeled with the corresponding winding terminal identified in FIG. 3. The bus conductors 52, 54, 56, 58, 60, 62, 64, 66 and 68 interconnect their respective bushing terminals as shown in FIG. 4 as well as in FIGS. 2 and 3.

Modifications to the bushing and bus conductor arrangements are within the scope of the invention. FIG. 5 illustrates a delta closure arrangement wherein the terminals 90 of the bushing 92 are reversed in relation to the terminals 48 of the bushing 36 shown in FIG. 4. The bus conductors 94, 96, 98, 100, 102, 104, 106, 108 and 110, which are shown in FIG. 5, interconnect the terminals of the bushings 92, 112 and 114 electrically in the same manner as the arrangement of FIG. 4. Changing the terminal positions of the other bushings is also within the contemplation of this invention.

Since a particular application of the furnace transformer may require a higher secondary voltage than that which is provided by paralleling each .separate phase winding, series or series-parallel combinations may be necessary. FIG. 6 illustrates a bushing and bus conductor arrangement in which the separate phase windings (three per phase in this illustration) are serially interconnected to increase the output voltage. The bus conductors 118, 120, 122, 124, 126, 128, 130, 132 and 134 serially interconnect the separate phase windings to form a delta connected secondary winding. Numerous other bus conductor arrangements may be used without departing from the teachings of the invention.

The orientation of the secondary bushings on the transformer casing may be modified considerably without departing from the spirit of the invention. FIG. 7. illustrates a bushing arrangement wherein the bushings 136 and 138 are oriented so that the flat side of the terminals of each bushing are in alignment with each other. For purposes of discussion, the bushings 136 and 138 will be referred to as being vertically oriented. Conversely, the bushing 140 is horizontally oriented. The three bushings are arranged in a substantially triangular pattern, that is, lines drawn between the centers of the bushings would form a triangle. Maximum symmetry of the bushings is obtained when the triangle formed by the imaginary lines is an equilateral triangle, although this is not necessary for proper operation. The bus conductors 142, 144, 146, 148, 150, 152, 154, 156 and 158 are arranged to form a delta closure which produces the electrical equivalent of the circuit shown in FIG. 3.

FIG. 8 illustrates a bushing arrangement wherein the secondary bushings 160, 162 and 164 are all horizontally oriented. The bus conductors 166, 168, 170, 172, 174, 176, 178, 180 and 182 are arranged to form a delta closure which gives the electrical equivalent of the circuit shown in FIG. 3. In this illustration, as well as in the other illustrations of preferred embodiments of the invention, the location of the specific phase winding terminal in relation to other terminals on the same bushing may be changed. Modifying the terminal locations might require new bus conductor arrangements, however, the modified arrangement is still within the contemplation of the invention.

The bushings of FIG. 9 illustrate a Wye-pattern bushing arrangement. The bushing 184 is vertically oriented and the bushings 186 and 188 are oriented obliquely to each other and to the bushing 184. The bus conductors 190, 192, 194, 196, 198, 200, 202, 204 and 206 form the delta closure which is electrically represented in FIG. 3.

The bushings of FIG. 10 illustrate an arrangement wherein the bushings 208 and 210 are horizontally oriented and the bushing 212 is vertically oriented. The bus conductors 214, 216, 218, 220,222, 224, 226, 228 and 230 are arranged to form a delta closure which gives the electrical equivalent of the circuit shown in FIG. 3.

The triangularly arranged bushings disclosed herein, together with other triangular arrangements contemplated hereby, may be used to achieve several important advantages. The delta closure is efficient due to the substantially balanced closure arrangement furnished by the relatively equal length bus conductors, as compared to prior art arrangements. Due to the simpler bends involved, the bus conductors may be prefabricated at the factory and installed in the field, thus providing a cost savings and reducing the chance of incorrect connections. Less bus conductor material is required, thus offering a cost reduction of the equipment. The overall space required by the delta closure is reduced due to the elimination of the compound bends required by prior art methods; bushing performance is enhanced due to the fact that their inner ends are submerged in the liquid transformer coolant; and the arrangement is automatically compatible with triangular load bus runs.

Since numerous changes may be made in the above described apparatus and difierent embodiments of the invention may be made without departing from the spirit thereof, it is intended that all of the matter contained in the foregoing description, or shown in the accompanying drawings, shall be interpreted as illustrative, rather than limiting.

We claim as our invention:

1. Electrical inductive apparatus comprising a casing having side walls and a cover plate, said casing enclosing high-voltage primary windings and high-current secondary windings, high-voltage bushings attached to the casing and connected to the primary windings, three high-current bushings attached to the casing and connected to the secondary windings, said high-current bushings comprising a plurality of substantially flat conducting terminals mounted in the bushing with their flat surfaces adjacent each other, said high-current bushings being positioned on the casing to form a triangular pattern bushing arrangement so that bus conductors may be connected between the bushings without crossing over other bus conductors.

2. The electrical inductive apparatus of claim 1 wherein the three high-current bushings are positioned on the transformer casing so that lines drawn between the centers of the high-current bushings will form a triangle, and the opposite ends of the separate secondary windings are connected to adjacent terminals on a high-current bushing.

3. The electrical inductive apparatus of claim 1 wherein the three high-current bushings are substantially similar and each has a first and second axis, said first axis being perpendicular to the flat surface of the terminals and parallel to the surface to which the bushing is mounted, said second axis being perpendicular to the first axis and parallel to the surface to which the bushing is mounted, two of the high-current bushings being oriented so that their first axes are coincident with each other and perpendicular to the first axis of the third high-current bushing.

4. The electrical inductive apparatus of claim 1 wherein the three high-current bushings are substantially similar and each has a first and second axis, said first axis being perpendicular to the flat surface of the terminals and parallel to the surface to which the bushing is mounted, said second axis being perpendicular to the first axis and parallel to the surface to which the bushing is mounted, two of the high-current bushings being oriented so that their second axes are coincident with each other and perpendicular to the second axis of the third high-current bushing.

5. The electrical inductive apparatus of claim 1 wherein the three high-current bushings are substantially similar and each has a first and second axis, said first axis being perpendicular to the flat surface of the terminals and parallel to the surface to which the bushing is mounted, said second axis being perpendicular to the first axis and parallel to the surface to which the bushing is mounted, all three of the high-current bushings being oriented so that their second axes are parallel to each other.

6. The electrical inductive apparatus of claim 1 wherein the three high-current bushings are substantially similar and each has a first and second axis, said first axis being perpendicular to the flat surface of the terminals and parallel to the surface to which the bushing is mounted, said second axis being perpendicular to the first axis and parallel to the surface to which the bushing is mounted, all three high-current bushings being oriented so that their first axes are parallel to each other.

7. The electrical inductive apparatus of claim 1 wherein the three high-current bushings are substantially similar and each has a first and second axis, said first axis being perpendicular to the flat surface of the terminals and parallel to the surface to which the bushing is mounted, said second axis being perpendicular to the first axis and parallel to the surface to which the bushings are mounted, the bushings being oriented so that their first axes intersect to form angles of approximately 8. The electrical inductive apparatus of claim 1 wherein the three high-current bushings are substan tially similar and each has a first and second axis, said first axis being perpendicular to the fiat surface of the terminals and parallel to the surface to which the bushing is mounted, said second axis being perpendicular to the first axis and parallel to the surface to which the bushing is mounted, said high-current bushings being oriented so that they have no coincident first or second axes.

9. The electrical inductive apparatus of claim 1 wherein the triangular pattern bushing arrangement is positioned on a side wall of the casing.

10. Electrical inductive apparatus comprising a casing having side walls and a cover plate, said casing enclosing a three-phase high-voltage primary winding and a three-phase high-current secondary winding, highvoltage bushings attached to the casing and connected to the primary winding, three substantially similar highcurrent bushings attached to a side wall of the casing with their inner ends contained within the fluid coolant of the apparatus and connected to said secondary winding, said high-current bushings comprising a plurality of substantially flat conductor terminals mounted in the bushings with their flat surfaces adjacent each other, said high current bushings each having a first and second axis, said first axis being perpendicular to the flat surface of the terminals and parallel to the surface to which the bushing is mounted, said second axis being perpendicular to the first axis and parallel to the surface to which the bushing is mounted, said high current bushings being positioned to form a triangular pattern bushing arrangement so that bus conductors may be connected between the bushings without crossing over other bus conductors.

11. The electrical inductive apparatus of claim 10 I wherein two of the high-current bushings are oriented 

1. Electrical inductive apparatus comprising a casing having side walls and a cover plate, said casing enclosing high-voltage primary windings and high-current secondary windings, highvoltage bushings attached to the casing and connected to the primary windings, three high-current bushings attached to the casing and connected to the secondary windings, said high-current bushings comprising a plurality of substantially flat conducting terminals mounted in the bushing with their flat surfaces adjacent each other, said high-current bushings being positioned on the casing to form a triangular pattern bushing arrangement so that bus conductors may be connected between the bushings without crossing over other bus conductors.
 2. The electrical inductive apparatus of claim 1 wherein the three high-current bushings are positioned on the transformer casing so that lines drawn between the centers of the high-current bushings will form a triangle, and the opposite ends of the separate secondary windings are connected to adjacent terminals on a high-current bushing.
 3. The electrical inductive apparatus of claim 1 wherein the three high-current bushings are substantially similar and each has a first and second axis, said first axis being perpendicular to the flat surface of the terminals and parallel to the surface to which the bushing is mounted, said second axis being perpendicular to the first axis and parallel to the surface to which the bushing is mounted, two of the high-current bushings being oriented so that their first axes are coincident with each other and perpendicular to the first axis of the third high-current bushing.
 4. The electrical inductive apparatus of claim 1 wherein the three high-current bushings are substantially similar and each has a first and second axis, said first axis being perpendicular to the flat surface of the terminals and parallel to the surface to which the bushing is mounted, said second axis being perpendicular to the first axis and parallel to the surface to which the bushing is mounted, two of the high-current bushings being oriented so that their second axes are coincident with each other and perpendicular to the second axis of the third high-current bushing.
 5. The electrical inductive apparatus of claim 1 wherein the three high-current bushings are substantially similar and each has a first and second axis, said first axis being perpendicular to the flat surface of the terminals and parallel to the surface to which the bushing is mounted, said second axis being perpendicular to the first axis and parallel to the surface to which the bushing is mounted, all three of the high-current bushings being oriented so that their second axes are parallel to each other.
 6. The electrical inductive apparatus of claim 1 wherein the three high-current bushings are substantially similar and each has a first and second axis, said first axis being perpendicular to the flat surface of the terminals and parallel to the surface to which the bushing is mounted, said second axis being perpendicular to the first axis and parallel to the surface to which the bushing is mounted, all three high-current bushings being oriented so that their first axes are parallel to each other.
 7. The electrical inductive apparatus of claim 1 wherein the three high-cuRrent bushings are substantially similar and each has a first and second axis, said first axis being perpendicular to the flat surface of the terminals and parallel to the surface to which the bushing is mounted, said second axis being perpendicular to the first axis and parallel to the surface to which the bushings are mounted, the bushings being oriented so that their first axes intersect to form angles of approximately 120*.
 8. The electrical inductive apparatus of claim 1 wherein the three high-current bushings are substantially similar and each has a first and second axis, said first axis being perpendicular to the flat surface of the terminals and parallel to the surface to which the bushing is mounted, said second axis being perpendicular to the first axis and parallel to the surface to which the bushing is mounted, said high-current bushings being oriented so that they have no coincident first or second axes.
 9. The electrical inductive apparatus of claim 1 wherein the triangular pattern bushing arrangement is positioned on a side wall of the casing.
 10. Electrical inductive apparatus comprising a casing having side walls and a cover plate, said casing enclosing a three-phase high-voltage primary winding and a three-phase high-current secondary winding, high-voltage bushings attached to the casing and connected to the primary winding, three substantially similar high-current bushings attached to a side wall of the casing with their inner ends contained within the fluid coolant of the apparatus and connected to said secondary winding, said high-current bushings comprising a plurality of substantially flat conductor terminals mounted in the bushings with their flat surfaces adjacent each other, said high current bushings each having a first and second axis, said first axis being perpendicular to the flat surface of the terminals and parallel to the surface to which the bushing is mounted, said second axis being perpendicular to the first axis and parallel to the surface to which the bushing is mounted, said high current bushings being positioned to form a triangular pattern bushing arrangement so that bus conductors may be connected between the bushings without crossing over other bus conductors.
 11. The electrical inductive apparatus of claim 10 wherein two of the high-current bushings are oriented so that their first axes are coincident with each other and perpendicular to the first axis of the third high-current bushing. 